The present invention relates to a method for controlling an internal combustion engine, particularly for motor vehicles. The principle of recirculating a portion of the exhaust gases of an engine back to the engine cylinders is known, equipping, for example, a motor vehicle. “Exhaust Gas Recirculation” is commonly referred to as “EGR”. Mixing exhaust gas with the admitted fresh air has an impact on the combustion of the fuel mixture. The presence of exhaust gases, which are inert to combustion, and have a high heat capacity, helps reducing the temperature in the cylinders. In a gasoline engine, it also reduces the risk of self-ignition of the mixture, which decreases rattling noises propensity. In addition, exhaust gases recirculation helps reduce pumping losses. The use of exhaust gas recirculation helps reducing the specific fuel consumption, making it a very interesting technology. We also know that in order to guarantee good conversion by the catalytic converter of the pollutants in the exhaust gases, the richness of operation needs to be close to 1, which means that the composition of the mixture of air and fuel is near to the stoichiometry. To minimize pollutant emissions, the major part of the engine operating conditions is thus guaranteed with a richness of 1, also called stoichiometric richness. An exception to this mode of operation is when the exhaust temperature is too high for operation at a richness of 1. These conditions are met when the power delivered by the engine is close to the engine maximum power available. In such conditions, the mixture is voluntarily enriched, which means that it has an excess of fuel in comparison to the stoichiometric mixture. The effect of such enrichment is to lower exhaust temperatures and make them acceptable.
The counterpart is an increase in the consumption of fuel and emission of pollutants. So the enrichment must be kept to a minimum. The value of the enrichment is thus defined for various operating conditions, defined for instance by the speed of rotation of the motor and the delivered torque.